Thin film electroluminescent (TFEL) display panels offer several advantages over older display technologies such as cathode ray tubes (CRTs) and liquid crystal displays (LCDs). Compared with CRTs, TFEL display panels require less power, provide a larger viewing angle, and are much thinner. Compared with LCDs, TFEL display panels have a larger viewing angle, do not require auxiliary lighting, and can have a larger display area.
FIG. 1 shows a conventional TFEL panel 10. The TFEL panel has a glass panel 11, a plurality of transparent electrodes 12, a first layer of a dielectric 13, a phosphor layer 14, a second dielectric layer 15, and a plurality of metal rear electrodes 16 perpendicular to the transparent electrodes 12. The transparent electrodes 12 are typically indium-tin oxide (ITO) and the metal electrodes 16 are typically Al. The dielectric layers 13, 15 to protect the phosphor layer 14 from excessive dc currents. When an electrical potential, such as about 200V, is applied between the transparent electrodes 12 and the metal electrodes 16, electrons tunnel from one of the interfaces between the dielectric layers 13, 15 and the phosphor layer 14 into the phosphor layer where they are rapidly accelerated. The phosphor layer 14 typically comprises ZnS doped with Mn. Electrons entering the phosphor layer 14 excite the Mn causing the Mn to emit photons. The photons pass through the first dielectric layer 13, the transparent electrodes 12, and the glass panel 11 to form a visible image.
Although current TFEL panels are satisfactory for some applications, more advanced applications require brighter higher contrast panels, larger panels, and sunlight viewable panels. One approach in attempt to provide adequate panel contrast under high ambient illumination is the use of a circular polarizer filter which reduces ambient reflected light. A circular polarizer filter operates best with a TFEL panel which is very specular. If the specularity of the metal rear aluminum electrodes 16 can be increased, then the efficiency of the circular polarizer filter will also increase.
It is well known in the art that the specularity of an object is directly inverse to the diffuse reflectance of that object. Thus, as the specularity of the panel increases, the diffuse reflectance decreases.